Shift in feather mite distribution during the molt of passerines: the case of barn swallows (Hirundo rustica)

Abstract

Feather mites show a high diversity of distribution patterns on the wings of birds, but we are currently unable to make precise predictions about the distribution of mites on a given bird at a given time. This is especially intriguing because factors such as air turbulence, humidity, or temperature are already recognized as shaping feather mite distribution. We hypothesize that feather mites, rather than responding to single factors, respond at the same time to different constraints when deciding where to live. To test this hypothesis, we studied the distribution of mites along the wings of barn swallows (Hirundo rustica L., 1758) in Europe before molting and in Africa during and after molt. Feather mite preferences shifted according to the stage of molt of the bird, with a pattern suggesting a clear compromise between being as close as possible to the non-molting distribution while avoiding the molt of the occupied feather and the early stages of growth of new feathers. Thus, we suggest that interacting factors, rather than single variables, must be studied to further advance the understanding of the distribution of feather mites on the wings of birds.